Ch. 15 Sensory Pathways

sensory pathway division

afferent

involuntary/voluntary motor pathway division

efferent

events along sensory pathway

stimulus arrives, depolarization of sensory receptors, if large enough and action potential is generated, triggers porpogation down axon to axon terminals

CNS processing

information is distributed to nuclei and centers in the spinal cord and brain

involuntary motor pathway

processing centers in the spinal cord or brainstem direct immediate response before sensation reaches cerebral cortex 

voluntary motor pathway

not immediate, signals are sent to cerebrum and need to be perceived then they can moderate, enhance, or supplement simple involuntary response 

perception in motor pathway

1% of arriving sensations are relayed to primary somatosensory cortex

sensory receptors

detects stimulus and sends it to the nervous system

sensation

act of detecting and being aware of arriving information and stimuli

perception

conscious awareness of a sensation

transduction

the process of converting stimuli into neural signals

receptive field

where stimulus is perceived, can’t get more specific than which field. when fields overlap, they’re less sensitive

adaptation

reduction of receptor sensitivity in the presence of constant stimulus

tonic receptors

always active, frequency increases during action potential, adapt slowly (pain)

phasic receptors

normally inactive, but become active for a short time when a stimulus is applied. They adapt quickly to changes in stimuli. don’t think about them until you do (tell you when stimulus is applied and when it stops, inactive in-between)

exteroceptors

provide information about external environment

proprioceptors

report positions of skeletal muscles and joints

interoceptors

monitor visceral organs and functions

sensory receptor classifications

determined based on how adaptive/sensitive they are and where they are

thermoreceptors

detect temperature changes. sensations conducted along same pathways that carry pain sensations. temp change felt relative to what the body is used to

thermoreceptor locations

free nerve endings in dermis, skeletal muscles, liver, and hypothalamus. sensations are sent to reticular formation in thalamus and the primary somatosensory cortex

tactile receptors in skin

6 types. allow us to feel and perceive everything our hands do

free nerve endings

tonic, basic on and off branching tips of sensory neurons that respond to touch, pressure, pain and temp

root hair plexus

phasic, basic, made up of free nerve endings stimulated by hair movement that wrap around hair follicle

tactile discs

phasic, fine touch and pressure receptors very sensitive to shape and texture

bulbous corpuscle

tonic, sensitive to deep pressure and skin distortion of the deep dermis

lamellar corpuscle

phasic, sensitive to deep pressure and high-frequency vibration

tactile corpuscle

phasic, sensitive to fine touch, pressure, and low-frequency vibrations (eyelids, lips, fingertips, nipples, external genitalia)

pain receptors w/ unmyelinated axon

sharp pain, triggers somatic reflexes, acutely and consciously aware of it

pain receptors w/ myelinated axon

burning, aching, dull, and chronic pain. know the pain is there, but not always acutely aware and can’t specifically pinpoint it

chemoreceptors

lead to changes in pH, CO₂, and O₂. in medulla and cardiovascular system

baroreceptors

sub-category of mechanoreceptors, monitor changes in pressure in an organ, free nerve endings that branch with elastic tissues, respond immediately to pressure changes. in digestive tract, lungs, blood vessels, colon, and bladder

proprioception

somatic sensation in skeletal muscles, tendons, ligaments and joints

proprioception type 1

muscle spindles

proprioception type 2

golgi tendon organs at junction of muscles fibers that aid in concentric and isometric movements under load 

proprioception type 3

joint capsules that detect changes in pressure, tension and movement within a joint

first-order neuron

sensory neuron that delivers sensations to CNS

second-order neuron

interneuron in spinal cord or brainstem the receives info from first-order neuron and takes signal to PNS

third-order neuron

neuron in thalamus that receives info from second-order neuron in order for sensation to reach our awareness

receptor level

sensory reception and transmission to CNS (detect stimuli)

circuit level

processing in ascending afferent pathways

perceptual level

processing in cortical sensory centers

decussation

crossing to opposite side of CNS

posterior root

receives signal from afferent division

anterior root

sends signals

spinothalamic pathway

anterior and lateral spinothalamic tracts. carries sensations of crude touch, pressure, pain and temp. crossing over occurs at spinal cord

anterior spinothalamic tracts

crude touch and pressure

lateral spinothalamic tracts

pain and temp

results of abnormalities in spinothalamic pathway

painful sensations that are no produced where they are perceived to originate (phantom limb)

posterior column pathway

gracile and cuneate fasciculus, carries sensations of fine touch, vibration, pressure and proprioception. crossing over occurs at gracile and cuneate fasciculus nucleus. axons enter medial lemniscus tract

spinocerebellar pathway

posterior and anterior spinocerebellar tracts. does not reach thalamus and our awareness. conveys info about positions of joints and their angles, muscles, and tendons and their kinematics in spaces from spinal cord to cerebellum

posterior spinocerebellar tracts

axons don’t cross to opposite side of spinal cord which gives full 3-D pic of where our limbs are in space without feedback from the environment (left brain controls right body)

motor tract

controls muscle tone and gross movements of neck, tunk, and proximal limb muscles

vestibular nuclei

aids in balance and spatial orientation

superior colliculi

controls reflexive responses to visual stimuli

inferior colliculi

controls auditory reflexes

reticular formation

coordinates muscles and muscular functions

corticospinal pathway

lateral, anterior and cortocobulbar tracts involved in voluntary control over skeletal muscles. bulk of pathways. conscious and subconscious motor commands

lateral corticospinal tract

controls limbs

anterior corticospinal tract

controls axial skeleton

cortocobulbar corticospinal tract

controls skeletal muscles from neck up

lateral pathway

rubrospinal tract. voluntary, skilled, and fine movements of the arms and legs

rubrospinal tract

involved in motor control, particularly with flexion of the arms.

medial pathway

medial and lateral reticulospinal, tectospinal and vestibulospinal tracts. control posture, balance, and gross movements of the axial and proximal muscles

medial and lateral reticulospinal tracts

medial- increases muscle tone and helps with voluntary and patterned movements like walking. lateral- inhibits voluntary movements and reduces muscle tone. 

tectospinal tract

involved in reflexive movements of the head and neck in response to visual and auditory stimuli

vestibulospinal tract

plays a crucial role in maintaining posture and balance during movement.